An external massif is, in the geology of the Alps, a place where crystalline rocks of the European plate crop out.
The massifs are composed of the basement of the former margin of the European plate, consisting of metamorphic and igneous rocks of Hercynian age or older.
The Mesozoic cover that was originally on top of these rock has mostly been detached by thin skinned thrusting about 40 to 25 million years ago (Ma).
[2] At some places along the Aarmassif, the Mesozoic cover is partly still lying conformally on top of the Hercynian basement rock, this Mesozoic is called the Infrahelvetic complex.
The uplift that brought the massifs to the surface involved thick skinned thrusting (the style of thrusting in which the basement is itself involved) and took place in a tectonic phase beginning around 19 million years ago.